Section 09 · Monograph

Methocarbamol

Reviewed Nov 2026FDA label

RobaxinMuscle relaxant

Indications

Adjunct to rest, physical therapy, and other measures for relief of discomfort associated with acute, painful musculoskeletal conditions (tablet and injection) — not FDA-indicated for spasticity due to CNS/upper motor neuron disease.FDA-labeled
Injection formulation only: adjunct (supportive, not primary) therapy in the control of neuromuscular manifestations of tetanus, used alongside standard tetanus management.FDA-labeled

Occasionally used off-label for other muscle spasm-related conditions (e.g., restless legs symptoms, adjunct in acute low back pain protocols) — limited high-quality evidence.Off-label

Exact mechanism not clearly established.
Effects thought to be related to general central nervous system (CNS) depression/sedative properties rather than a direct effect on muscle.
Methocarbamol does not directly relax tense (spastic) skeletal muscle in humans; it has no direct action on the contractile mechanism of striated muscle, the motor end plate, or the nerve fiber.

Tablets (500 mg): initial dosage 1500 mg (3 tablets) four times daily; maintenance dosage generally 1000 mg (2 tablets) four times daily.
Tablets (750 mg): initial dosage 1500 mg (2 tablets) four times daily; maintenance 750 mg every 4 hours (1 tablet) or 1500 mg three times daily.
General regimen: up to 6 g/day (up to 8 g/day in severe conditions) for the first 48-72 hours, then reduce to a maintenance dose of about 4 g/day.
Injection: 1 g (10 mL) IV or IM; may repeat every 8 hours if needed, up to 3 g/day, for no more than 3 consecutive days (except when treating tetanus). IV push should not exceed 3 mL/minute; patient should remain supine during and for a short period after IV administration due to risk of hypotension/syncope.
Tetanus (injection): may give up to 24 g/day, dosed per severity and clinical response, not subject to the standard 3-day limit.

Renal impairment: avoid injectable formulation given the polyethylene glycol vehicle; use tablets with caution and dose adjustment as needed.

Injection: known or suspected renal pathology is a contraindication for the injectable form specifically because of the polyethylene glycol 300 vehicle, which is concentrated by the kidney and could aggravate renal impairment.
Known hypersensitivity to methocarbamol or any component of the formulation.

CNS depressants (alcohol, sedatives, opioids, benzodiazepines) — additive sedation/CNS depression; caution regarding driving/operating machinery.
Pyridostigmine bromide — methocarbamol may inhibit the effectiveness of pyridostigmine; use with caution in patients with myasthenia gravis receiving anticholinesterase agents.
Anticholinesterase agents — potential interference, as above.

Common: drowsiness/sedation, dizziness/lightheadedness, headache, nausea, blurred vision, metallic taste, flushing (with IV administration), mild transient hypotension with IV use.
Serious: syncope, seizures (or seizure-like activity), anaphylactoid reactions/hypersensitivity, injection-site reactions including thrombophlebitis and, rarely, sloughing/extravasation injury with IV administration, and (rarely) leukopenia.
Overdose can cause CNS depression, including drowsiness progressing to lethargy, dizziness, blurred vision, hypotension, seizures, and coma.

Level of sedation/CNS depression and mental alertness (advise against driving/hazardous tasks until effects known).
Blood pressure, particularly during and after IV administration (risk of hypotension/syncope).
Renal function prior to and during IV therapy given PEG-300 vehicle concerns.
IV/injection site for signs of thrombophlebitis or extravasation.
Duration of use — limit continuous therapy per labeling except in tetanus management.

Pregnancy: older FDA Pregnancy Category C; adequate and well-controlled human studies are lacking; there have been very rare postmarketing reports of fetal/congenital abnormalities following in utero exposure, though causality is not established. Use during pregnancy only if clearly needed and if potential benefit justifies potential risk to the fetus.
Lactation: not known whether methocarbamol or its metabolites are excreted in human milk; caution is advised when administering to a nursing mother given the potential for sedation in the infant.